WAITID(2) System Calls WAITID(2)

NAME

waitid - wait for child process to change state

SYNOPSIS

#include <wait.h>

int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

DESCRIPTION

The waitid() function suspends the calling process until one of its child
processes changes state. It records the current state of a child in the
structure pointed to by infop. It returns immediately if a child process
changed state prior to the call.


The idtype and id arguments specify which children waitid() is to wait
for, as follows:

o If idtype is P_PID, waitid() waits for the child with a
process ID equal to (pid_t)id.

o If idtype is P_PGID, waitid() waits for any child with a
process group ID equal to (pid_t)id.

o If idtype is P_ALL, waitid() waits for any child and id is
ignored.


The options argument is used to specify which state changes waitid() is
to wait for. It is formed by bitwise OR operation of any of the following
flags:

WCONTINUED
Return the status for any child that was stopped and has
been continued.


WEXITED
Wait for process(es) to exit.


WNOHANG
Return immediately.


WNOWAIT
Keep the process in a waitable state.


WSTOPPED
Wait for and return the process status of any child that
has stopped upon receipt of a signal.


WTRAPPED
Wait for traced process(es) to become trapped or reach a
breakpoint (see ptrace(3C)).


The infop argument must point to a siginfo_t structure, as defined in
siginfo.h(3HEAD). If waitid() returns because a child process was found
that satisfies the conditions indicated by the arguments idtype and
options, then the structure pointed to by infop will be filled by the
system with the status of the process. The si_signo member will always be
equal to SIGCHLD.


One instance of a SIGCHLD signal is queued for each child process whose
status has changed. If waitid() returns because the status of a child
process is available and WNOWAIT was not specified in options, any
pending SIGCHLD signal associated with the process ID of that child
process is discarded. Any other pending SIGCHLD signals remain pending.

RETURN VALUES

If waitid() returns due to a change of state of one of its children and
WNOHANG was not used, 0 is returned. Otherwise, -1 is returned and
errno is set to indicate the error. If WNOHANG was used, 0 can be
returned (indicating no error); however, no children may have changed
state if infop->si_pid is 0.

ERRORS

The waitid() function will fail if:

ECHILD
The set of processes specified by idtype and id does not
contain any unwaited processes.


EFAULT
The infop argument points to an illegal address.


EINTR
The waitid() function was interrupted due to the receipt of a
signal by the calling process.


EINVAL
An invalid value was specified for options, or idtype and id
specify an invalid set of processes.

USAGE

With options equal to WEXITED | WTRAPPED, waitid() is equivalent to
waitpid(3C). With idtype equal to P_ALL and options equal to WEXITED |
WTRAPPED, waitid() is equivalent to wait(3C).

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+

SEE ALSO

Intro(2), exec(2), exit(2), fork(2), pause(2), sigaction(2), ptrace(3C),
signal(3C), wait(3C), waitpid(3C), siginfo.h(3HEAD), attributes(7),
standards(7)

June 8, 2018 WAITID(2)